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 (Last modification: 04. Mar. 2009)

Substratspezifität von Flavonoid 3'5'-Hydroxylasen, und metabolisches Netzwerk ("metabolic grid")

Zitat: Kaltenbach et al. (1999)

Introduction

     Plants contain at least two types of P450-dependent flavonoid hydroxylases. One performs a single hydroxylation in the 3'-position (F3'H).of flavonoids, and the second performs two hydroxylations, both in the 3'- and the 5'-position (F3'5'H). cDNA clones for F3'5'H have been described from a few plants; they belong to the CYP75 family of P450 proteins. If you look a bit more closely on what is known about these enzymes, you'll notice that there are more open questions than you would think. We cloned the flavonoid hydroxylase from Catharanthus roseus in order to investigate some of the questions. The protein was expressed as fusion protein with the P450 reductase in E. coli and the function was identified: it is a 3',5'-hydroxylase (F3'5'H) with broad substrate specificity. A surprising finding from immunohistochemical analyses is that the expression of the F3'5'H is cell-type specific and different from that of CHS (Kaltenbach et al., 1999). It had been proposed previously that flavonoid biosynthesis involves a 'grid-type' network with intracellular compartmentation and different pathways with common intermediates. Our results are consistent with a conclusion that intercellular transport of substrates and/or intermediates may be an important component of the compartmentation.

The text below summarizes some of the results described in the publication.

Beide Proteine wurden heterolog in E. coli als translationale Fusionen mit der P450-Reduktase aus C. roseus exprimiert.

Es ist interessant, dass Flavone und Flavanone gute Substrate sind, während die Flavonole und Dihydroflavonole eindeutig schlechter akzeptiert werden. Eindeutig ist auch, dass monohydroxylierte Moleküle besser sind als Substrate, die bereits zwei Hydroxyl-Gruppen tragen (3',4'-hydroxyliert). Aber die Präferenzen für Flavone und Flavanone sind gleich.

Welches ist nun das physiologische Substrat? Das ist, zu mindestens auf der Basis solcher Daten nicht so einfach zu entscheiden.